It is well-known that a common source of injury to medical workers is needlestick injury. Needlestick injury occurs when a contaminated needle accidentally cuts a medical worker. Therefore, it is known to provide a needle containing medical device (typically a syringe) with a needle that is retracted into the syringe body after use to reduce or eliminate needlestick injury.
Another advantage in providing a retractable needle is to prevent the needle from being reused.
There are many types of mechanisms to enable a medical needle to be retracted into the syringe body.
One type of mechanism has the needle biased by a small helical spring. The needle is prevented from shooting back into the syringe body by some form of needle holding mechanism. The plunger contains some form of cutting mechanism, and when the plunger is pushed hard against the front of their syringe, the cutting mechanism cuts the needle holding mechanism to enable the needle to be shot back into the syringe body. This type of arrangement can be called a “cutting” arrangement.
Another type of mechanism does not require a spring around the syringe. Instead, the plunger is under vacuum. When the plunger is pushed hard against a front of the syringe, the plunger seal decouples from the front of the plunger and the plunger seal also attaches to the needle. Once the plunger seal is released from the front of the plunger, the vacuum in the plunger will suck back the plunger seal+the attached needle.
Another type of arrangement uses a spring that is behind the plunger seal such that as the plunger is pushed forwardly, the spring is tensioned. Again, as the plunger is pushed hard against the front of the syringe, the front of the plunger couples with the needle and the spring then pulls the plunger+the needle back into the syringe body.
A reliable mechanism is described in our earlier international patent application PCT/AU01/00183. This mechanism contains a needle which is biased by a small helical spring. The needle is attached to a needle holder. The needle holder is held in place against the bias of the spring by a small holding member that contains an outer part and an inner part that are separated by a frangible portion. When the plunger is pushed against the front of the syringe, the plunger will push the outer part forwardly while the inner part cannot move and this causes the frangible portion to break. Once this happens, the needle shoots back into the plunger body and pierces through the relatively thin plunger seal by the bias of the spring. This type of mechanism can be seen as a “stretch and break” mechanism as opposed to a cutting mechanism and is more reliable in use.
With needle containing medical devices such as syringes, irrespective of whether the syringe contains a retraction mechanism, there is often the need to replace the needles. As an example, when injecting the fluid, a larger diameter needle can be attached to the syringe to draw the fluid into the syringe body more quickly. Because the larger diameter needle can cause more pain to a patient, once the fluid is in the syringe body, the larger diameter needle can be removed and a smaller injecting needle is attached.
Attachment and removal of needles can cause needlestick injury, and even if the needle is not contaminated, a needlestick injury can still be quite painful. Therefore, there would be an advantage if it were possible to replace needles while reducing needlestick injury.
As syringes with shoot back needles are becoming more popular, these syringes will also require the needles to be replaced. However, syringes with shoot back mechanisms have the needle fixed to some part of the shoot back mechanism and replacement of the needle is not possible. Also, there is a danger that if the needle is made replaceable, this will make the shoot back mechanism less reliable or even in operable. Therefore, there would be an advantage if it were possible to have a needle containing medical device of the type where the needle can be retracted after use and where the needle can also be replaced prior to retraction and without unnecessarily interfering with the efficiency of the retraction mechanism.
Many syringes that do not have a retraction mechanism allow the needle to be replaced. This is a very conventional but suffers from the disadvantage that the parts can be quite small and removing the needle from the front of the syringe can be quite difficult especially if wearing gloves, if the surfaces are wet or contaminated and the like. Therefore, there would be an advantage if it were possible to provide a design that would enable needles to be removed and replaced in a more convenient manner.
It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.